Relay



R. GUMLEY Filed Ma 7 941 SLEEVE OF COPPER MAGNET/c SLEEVE OR R. H. GU VPatented Oct. 31, 1944 RELAY Robert H. Gumley, Whitestone, N. Y.,assignor to Bell Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation of New York Application May 7, 1941,Serial No. 392,281

3 Claims. (Cl. 175-21) This invention relates to relays and moreparticularly to the structure of relays for the protection of contactsin the energizing circuits thereof.

It has been found by experimentation and by experience with respect tocircuits in operation in commercial use that in some instances relaycontacts become welded together due to excessive current transmittedthereover for the operation of relays. such relays and the batterypotential employed did not indicate that such welding of the con tactsshould have occurred. From observations made it appeared that thewelding of contacts occurred in many instances when such contacts werein the operating circuits of relays having copper sleeves surroundingtheir cores for securing delay action.

The tendency of contacts to weld together under such conditions has inthe past been obviated by the use of palladium contacts and by theintroduction of a resistance-condenser network in shunt of the windingof the relay having the copper sleeve. In considering a simpler methodof preventing contact welding under the conditions above described,oscillograms were taken on a high speed oscilloscope of the closure ofcontacts connected into the operating circuit of a relay.Theseoscillograms showed that when the contacts closed the operatingcircuit of any relay, high current surges lasting for a fraction oi amicrosecond were produced. Usually these surges were of the order of oneampere or less and, therefore, of insufllcient amperage to causewelding. However. when the relays observed were equipped with coppersleeves, these surge currents were found to be considerably greater thanone ampere and caused welding in many cases.

The solution of the problem of contact welding appears, "therefore, todepend entirely upon the provision of some means which will restrict themagnitude of the surge currents on contact closure. Since it is believedthat the high surge currents produced in contacts controlling theoperating circuits of copper-fsleeved relays is probably due to theeii'ect of the-copper sleeves in reducing the inductance of the relaywindin s, the provision of means in the relays which will raise theinductance of the windings to these high surge currents on contactclosure would, therefore, prevent contact welding.

It is, therefore, the object of the invention to provide means in acopper-sleeved relay to raise the inductance of the relay winding at theinstant of closure of the operating circuit thereof,

.to thereby obviate the welding of the circuit closing contacts.

To attain this object and as disclosed in the The resistance loadoffered bysingle figure of the drawing, the applicant has placed a thinsheet of magnetic material, such as Permalloy, formed into a sleeve overthe copper sleeve and under the relay winding. As disclosed in thedrawing, the relay in accordance with the invention has a copper sleeveI surrounding the core 2, a sleeve 3 of Permalloy approximately 6 milsin thickness and the winding 4 placed over the Permalloy sleeve. Therelay is assumed to be operable in a circuit including the battery 5 andthe contacts 6 of another relay. 1

A relay constructed in this manner having a copper sleeve it" thick, atPermalloy sleeve .006" in thickness and a winding of 9,000 turns of wirewith a resistance of 640 ohms, was found by the oscilloscope to draw asurge current of one ampere across the contacts in the operating circuitwhen 60 foot leads were used in the circuit and one ampere on a shortercircuit using 8 foot leads as compared with a standard relay of the samecharacteristics but without the Permalloy sleeve which drew a surgecurrent of 2.5 amperes in a circuit of 60 foot leads and 1.6 amperes ina shorter circuit of 8 foot leads. It will be noted that the relaymodified in accordance with the invention, that is, having the Permalloysleeve, does not draw .a surge current of over one ampere, a value whichis not high enough to cause contact welding.

The present invention has been considered primarily with respect topreventing the welding or locking of contacts controlling the operatingcircuits of relays having copper sleeves, but it may also be useful inthe solution of other contact problems such as in the reduction ofcontact erosion.

What is claimed is:

1. In an electromagnetic device, a core having a normally open magneticcircuit, a short-circuited winding surrounding said core, an operatingwinding surrounding said short-circulted winding and a foil of magneticmaterial having 5 high permeability interposed between said windings.

2. In an electromagnetic device, a core having a normally open magneticcircuit, a short-circuited winding surrounding said core, an operatingwinding surrounding said short-circuited winding and a foil of Permalloyinterposed between said windings.

3. In an electromagnetic device, a cord having a normally open magneticcircuit, a copper sleeve surrounding said core, an operating windingsurroundlng said sleeve and a sheet 01 Permalloy

